Some questions about aspects of junk rig design

  • 29 Jul 2018 02:43
    Reply # 6403023 on 6401411
    Bill F wrote:

    That's just what I was looking for, lol, I'm so used to googling for info piecemeal on the JR  and putting it together myself I never even thought of the JRM.


    That's one of the reasons I like to get the paper magazine.  Somehow the contents seem to stick in my mind better than reading on line.  In fact, when I used to get the magazine on line, I'd sometimes forget to finish it.  (Of course, now that I'm involved in editing, every article tends to be etched firmly into my brain!!)
  • 27 Jul 2018 17:00
    Reply # 6401411 on 6392588
    Deleted user

    Thanks David

    That's just what I was looking for, lol, I'm so used to googling for info piecemeal on the JR  and putting it together myself I never even thought of the JRM.

    I think I'm going to put them all on my phone so I'll have them on hand any time I get a few minutes to read.


    Bill F


  • 26 Jul 2018 20:40
    Reply # 6399772 on 6398690
    Deleted user
    Bill F wrote:

    I'd certainly try the Aero Junk, the ones on Oryx look interesting, I wish a few more had been built or that at least some info on how the ones on Oryx worked out was available. I suppose I should see if Paul McKay has any info He'd be willing to share, there doesn't seem to be much here on the site, or at least that I can find, but then my search skills aren't that great.

    Bill

    Have a look at the latest JRA Magazine. There is a very good article on the Aero Junk written by Paul McKay. He also has a sheeting system with I think only a single sheet from the aft end of the boom which would make the Aero Junk suitable for a proa.
  • 26 Jul 2018 02:32
    Reply # 6398690 on 6392588
    Deleted user

    Hi Mark

    I'm currently working on a 5m proa with a flat bottom and multiple mast steps so I can test out different rigs, it's drawn with a 55 sq ft crabclaw, I'm looking to put a 75-100 sq ft junk on it. I should have a better idea of how a flat bottom works on a proa after I get it in the water.  That's why I've been spending so much time here, waiting for epoxy to dry, I have to stay far enough away that I can't stick my fingers in it :)

    It'll have a leeboard on the ama that slides nearly 8 feet fore and aft, or I guess that would be fore and fore :) and since it will kick-up it could be rotated to move the CLR even further, the idea being to balance the boat around whatever sort of sail I try rather than being stuck with a certain sort of sail, also to keep rudder loads down so I don't need monster rudders. I may try to attach some sort of trim tabs so I can steer from the leeboard as well, I don't hold out much hope for that working well.

    I've already got another proa on the drawing board, well, bouncing around my noggin :) other than the length and beam of the Vaka, 28' X 28" at the waterline nothing is really decided yet though, it mostly depends on how the experiments with the proa I'm building now go.

    I'd certainly try the Aero Junk, the ones on Oryx look interesting, I wish a few more had been built or that at least some info on how the ones on Oryx worked out was available. I suppose I should see if Paul McKay has any info He'd be willing to share, there doesn't seem to be much here on the site, or at least that I can find, but then my search skills aren't that great.

    I don't think the Deep V is very sensible on a boat that already has a lot of WSA, but there's a 5m  production proa being built in Poland  that's a deep V, beautiful boat. http://www.pjoa.eu/ 

    I've watched some video of one doing 10 knots in some very lumpy water and I'm impressed. Really don't see any value in a deep v on a cruising proa though.

    Well, the epoxy should be dry enough that it won't stick to my finger, back to work :)


    Bill

  • 25 Jul 2018 13:44
    Reply # 6397413 on 6392588

    Bill,

    I think the Aero-Junk is ideal for a proa, so no need to look at alternatives.

    It is well balanced, and symmetrical on both shunts.

    I would choose the rig, then design the hull(s) and boards / rudders to suit.  A deep V is definitely a wrong direction.  With a flat bottomed, I guess that the hulls are so fine the end is not going to pound unduly.

    Cheers Mark 

  • 24 Jul 2018 03:02
    Reply # 6394898 on 6392588
    Deleted user

    Thanks David :)


    I enjoyed the "Weaverbirds new sail " thread, a lot of great info and Ideas there, and the pics, it's actually just what I needed to move forward on a Proa specific junk rig that has dedicated windward/leeward sides.

    That's why I was asking about rise, glad to hear I had that one right, this just might be doable.

    Funny part is, apparently I was trying to make it work on the bad shunt(s) :)


    The concept is pretty basic at the moment and only covers parallel panels:

    wishbone battens with one way batten hinges (See A Below) about 1/3 of the chord from each end on the lee side of the wishbones, hinges open to leeward making wishbone wider at that area, may need to use two at each end.

    sailcloth on leeward side only similar to an aero-junk, OR, wingsail.

    Sail hauled across  mast from shunt to shunt, something like a Yard Hauling Parrel?

    mast line just aft of luff side batten hinges or between if two batten hinges are used.

    sheets for each shunt run through deadeyes in the windward batten and attach at the back of the batten hinges (In between batten hinges if two are used at each end), pull on the sheet is on the lee batton.

    wind pressure forces the batten hinges at the mast line open giving camber at leading edge.

    Sheets attached to batten hinges at leach close hinges leaving aft ~50% of the sail flat.

    it could even tack :)


    Headsail is problematic but, 

    Headsail Concept 1)

    a pair of roller reefing headsails, one for each shunt on their own yard/halyard, 2 panels, cone shaped centre batten rolo-reefs both panels simultaneously, or a single panel rolo reefing from the lower edge.


    Headsail Pipe dream, er, I mean concept 2)

    wingsail, run fabric all the way around the wishbones and fabric extends over top wishbone/yard and back down inside the sail, wishbone tilts on each shunt fabric attached to mast so when the sail is hauled across the mast fabric pulled tight at the luff and released at the leach so the wishbone/yard can tilt, I suppose it could be flat topped but I'd like a bit of an angle even if only because it would look better


    pretty barebones yet and i doubt it makes much sense except to me.


    A) one way batten hinges would be similar to those that David developed, I'd make the battens themselves out of wood, rectangular, hinges would be rectangular aluminum tubing slid over the battens, the hinge would be hardwood to start off with, with taper on only one side and probably not much. 

     I don't think twisting in the batten pockets should be a problem with wishbones.


    A few things that don't really fit in or need to be addressed:

    Headsail concept 1 might be detachable for use as stormsail since it would have it's own yard and halyard anyway, let you drop the sail bundle on deck for least windage and lowest center of gravity.

    weathercocking could be a real problem if one caught a gust at the wrong moment.

    rope stops at the mast lines might be tightened/loosened to change camber of the rig, if not on the fly than fairly quickly.

    The wingsail route would eliminate a lot of drag, the Aero_junk route could look pretty amazing though :) that's always important.


    needs a lot more thought, not to mention a fair amount of luck and a couple minor miracles.


    Bill

    Last modified: 24 Jul 2018 03:07 | Deleted user
  • 23 Jul 2018 15:17
    Reply # 6393712 on 6392588
    Anonymous wrote:

    Hi All

    There are a few things I'm a bit shaky on so I started this thread to ask for ideas and advice.

    1) Rise, the battens slope up from luff to leach, as far as I can tell the only reason for rise is to manage batten stagger when reefing and that it has no real effect on sail efficiency, is this the case?

    Correct.

    2) is there a list of the pros and cons of the different styles of junk rig available somewhere? for instance I've read that the broadhead has lots of power but isn't very weatherly

    I don't think there is such a list. Maybe there should be ( a little project for someone to pick up?). I'm just going to put in a little sales pitch here for the sail I made for Weaverbird - quite high AR, with a short yard at a low angle. This is the easiest junk rig to handle, and the best overall performing, taken all round, of any that I've built over the years (except for the soft wingsails, which do perform better, but take a lot more work to make).

    3) is there any downside to putting the sail directly on the mast like the aero-junk instead of hanging it on one side?

    The downside is that the mast is always adding drag, and always feeding turbulent air to the sail, whereas with the sail to one side, at least you get one good tack with the mast to leeward and half-buried in the sail.

    I'm sure there'll be more, the rig has been rattling around the inside of my noggin for months now :)


    Bill


    Last modified: 23 Jul 2018 15:18 | Anonymous member
  • 22 Jul 2018 19:57
    Message # 6392588
    Deleted user

    Hi All

    When I made the polytarp Hassler/McCloud rig for Bottoms Up I just slapped it together to see how it worked, I figure things out better if I can get my hands on them and kick the tires than by I do by reading/researching.

    my thoughts at the time were that a properly made sail would work at least 25% better than the quick and dirty polytarp rig, now I wonder if I could stand having 25% more fun :)

    there are a few things I'm a bit shaky on so I started this thread to ask for ideas and advice.

    1) Rise, the battens slope up from luff to leach, as far as I can tell the only reason for rise is to manage batten stagger when reefing and that it has no real effect on sail efficiency, is this the case?

    2) is there a list of the pros and cons of the different styles of junk rig available somewhere? for instance I've read that the broadhead has lots of power but isn't very weatherly

    3) is there any downside to putting the sail directly on the mast like the aero-junk instead of hanging it on one side?

    I'm sure there'll be more, the rig has been rattling around the inside of my noggin for months now :)


    Bill

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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